The invention relates to a device for conserving power in a piston compressor, in particular for generating compressed air in a motor vehicle, having a piston arranged in an axially movable manner in a cylinder for generating compressed air, which enters a compression chamber of the cylinder for compression via at least one intake valve, wherein the intake valve interacts with pressure-controlled measures for conserving power.
The area of application of the invention extends primarily to reciprocating piston compressors for motor vehicle construction, especially commercial vehicle construction. Such compressors are used primarily to produce compressed air for compressed air systems in the motor vehicle.
To control the delivery rate of such piston compressors and to control the pressure in downstream loads, e.g. a brake system, devices for conserving power are widely known. These devices open the intake valve of the piston compressor when a predetermined pressure is reached and said pressure acts as a control pressure on a mechanical actuating element for the opening of the intake valve. Devices of this kind are widely known as “governor” devices.
As an alternative to such governor devices, DE 33 29 790 A1 discloses a technical solution according to which the suction lamella of the compressor is moved parallel to the plane of the valve carrier between a pumping position and an idling position by way of an actuating piston guided in the valve carrier. The suction openings of the compressor are in overlap with the suction lamella in the working position, whereas they are at least partially exposed in the idling or cutoff position. In this position, the piston of the compressor, which continues to operate, idles, that is to say air is drawn out of the suction chamber of the cylinder head, through the at least partially open suction openings, into the compression chamber and pushed back into the suction chamber through the suction openings. At the same time, however, a certain compression work continues to be performed in order to force a small proportion of air into the compression chamber during the compression stroke through the compression openings, which are open with respect to the compression chamber, wherein the pressure valve on the upper side of the valve plate opens up at a certain pressure level, as before. Compressed air passes out of the pressure chamber into the pressure regulator and is exhausted to atmosphere there via a relief valve.
This means therefore that a proportion of the air drawn in during the suction stroke leaves the cylinder chamber through the suction openings, while a proportion of the air which is present as before is expelled through the compression openings.
During this operating state, the lubricating oil in the crankcase has an increased tendency to creep upward along the piston rings due to the reduced pressure level in the compression chamber. The result is that the lubricating oil can ultimately enter the compression chamber and contribute to increased enrichment of the air with lubricating oil. In the case of prolonged operation at high temperatures, an increased incidence of carbon consequently has to be expected.
When the suction valve is open, i.e. when the suction lamella is in the idling position, suction work continues to be performed as operation of the piston compressor continues, that is to say air is drawn into the compression chamber of the compressor via the suction line, the open suction port and the suction valve, which is in the idling position, and is at least partially expelled again into the suction line if the piston of the compressor is performing compression work. The air drawn into the compression chamber is loaded with oil particles, which creep along the piston rings in the direction of the compression chamber due to the reduced pressure level in the cylinder chamber. This air loaded with oil particles is at least partially expelled again through the suction line, and the lubricating oil accumulates and then subsequently crosses over in a surge into the pressure line when there is a switch to the delivery mode.
If there is a turbocharger connected to the suction line in parallel with the piston compressor, generating a certain vacuum within the suction line by its suction effect, there is furthermore the risk that the oil particles in the air in the suction line will enter the turbocharger and contribute there to severe coking Such coking is, of course, highly undesirable.
FR 1 098 045 A describes a piston compressor, the suction valve of which has an actuating mechanism that serves to hold the valve open. This is a tappet which acts on the suction valve and which carries a piston that can be acted upon by the pressure in the pressure reservoir connected to the compressor, such that, after a pressure threshold is exceeded, the tappet is moved by the piston and, accordingly, the suction valve is opened. Provided outside the piston compressor, in the suction line thereof, is a nonreturn flap which opens when a vacuum arises in the suction line in order to draw air into the piston compressor. The pressure valve of the piston compressor is unaffected by the actuation of the suction valve, which is always in a position ready for operation, with the result that a certain compression work is always performed, even in the idling position of the suction valve. As in the case of the prior art solution discussed above, the pressure valve opens above a certain pressure level, as a result of which compressor work is performed. Owing to the reduced pressure level in the compression chamber in the idling position, there is the problem, even with designs of this kind, that the lubricating oil can flow upward along the piston rings, i.e. into the compression chamber, and hence that there is enrichment of the air with lubricating oil. Moreover, the nonreturn flap gives rise to throttling losses which have a disadvantageous effect on the efficiency of the compressor. Taking this as a starting point, it is the object of the present invention to provide a device for conserving power in a piston compressor, by which power conservation that is as complete as possible is achieved in the cutoff or idling phase and that lubricating oil cannot unnecessarily enter the compression chamber from the crankcase and contribute there to oil enrichment of the air in the suction line.
This and other objects are achieved according to the invention by a device for conserving power in a piston compressor, in particular for generating compressed air in a motor vehicle, having a piston, which delimits a compression chamber, for generating compressed air, which, originating from the ambient environment, enters the compression chamber for compression via at least one suction port formed on a cylinder head cover and via an intake valve array arranged on a valve plate. For the purpose of conserving power, a pressure-dependently acting idling device is provided for the intake valve array, which is provided with an associated suction lamella and can be rotated by an actuator between a working position overlapping at least one suction opening and an idling position exposing, at least in part, the at least one suction opening. The actuator actuates the suction lamella in a coordinated manner such that, in the idling position, the lamella exposes the at least one suction opening in the valve plate while simultaneously closing adjacent pressure valve cross sections, at least partially, and blocks the suction port on the cylinder head cover by way of a slider in order to form an increased dead space in the region of the cylinder head.
The invention incorporates the technical teaching that the actuator actuates the suction lamella of the valve plate in a coordinated manner in such a way that, in the idling position, the lamella at least partially closes the at least one pressure valve opening in the valve plate or a comparable component while simultaneously exposing adjacent suction valve cross sections, and blocks the suction port on the cylinder head cover or a comparable component by way of a slider or the like in order to form an increased dead space in the region of the cylinder head.
Optimization of power conservation is achieved by way of the movement of the suction lamella into the open position being performed in the idling position and by way of the simultaneously performed, at least partial closure of the suction port on the cylinder head cover by the slider within the cylinder head. In the idling phase, the movable suction lamella in combination with the slider ensures that the suction line and, where applicable, filters and compressor systems connected to the suction line, remain unaffected by the continued idling of the piston. By means of the simultaneous, at least partially performed closure of the at least one pressure valve cross section of the piston compressor, it is furthermore ensured that there is no unnecessary discharge of air. As a result, all that is necessary is to draw in a small volume corresponding to the leakage losses via a check valve, preferably situated on the slider, when the piston of the compressor performs a suction movement in the idling position of the suction lamella. When the pressure openings of the compressor are fully closed, the additional quantity of air to be drawn in from the suction line is reduced to the actually existing leakage volume, also referred to as blow by, in the compression chamber of the cylinder.
The suction lamella, in the form of a sliding or rotary lamella, can be moved with the aid of the actuator, with control by a pressure regulator or by a control signal provided in some other way, out of its working position into the idling position, in which the at least one suction opening is either partially or completely exposed, such that the air drawn into the compression chamber can flow back into the suction chamber. The power conservation that can be achieved by this measure is of the order of about 60%.
The solution according to the invention ensures that no unnecessary air volume is displaced on the pressure side of the compressor. Especially in the case of turbochargers or compressors connected in parallel to the suction line of the piston compressor, the occurrence of coking in these at high temperatures due to the intake of air loaded with lubricating oil is also prevented. Moreover, the solution according to the invention does not have a disadvantageous effect on the efficiency of the compressor in the delivery phase, and therefore throttling losses are avoided.
The suction lamella is designed in such a way that it operates without friction. As a result, there is no wear between the suction lamella and the valve plate, even when there is very little lubricating oil in the compression chamber. Thus, this design is particularly suitable for compressors with reduced oil discharge and for oil-free compressor types.
It is advantageous if the suction lamella is designed in such a way that the pressure openings are completely or partially closed in the idling phase, depending on requirements. Unnecessary movement of a proportion of the volume of air into the pressure chamber thus does not occur. Only if a certain residual air delivery to avoid icing or soiling is desired is partial opening of the pressure openings in the valve plate set. Moreover, the closure of the suction port leads to a certain backpressure in the compression chamber, which contributes to keeping the lubricating oil out of the crankcase. The partial or complete coverage of the suction openings thus contributes to a further optimization in the power conservation that can be achieved.
In a preferred embodiment of the invention, the actuator, which is activated, preferably pneumatically, to move the suction lamella and the slider, acts substantially parallel to the plane of the valve plate and has an actuating piston that can be subjected to a control pressure. Here, the actuating piston can be guided in a bore in the cylinder head cover, which can be formed in the cylinder head cover in a casting process.
The actuating piston preferably acts by way of a driver pin extending through the bore on an actuating member, which can rotate the suction lamella between the working position and the idling position, and on the slider, which closes the suction port.
According to a preferred embodiment, the slider, which closes the suction port in the cylinder head cover, is designed as a pivoted slider pivotally attached thereto and is situated within the cylinder head cover.
The slider is furthermore preferably provided with a minimum air valve in the region that closes the suction port. According to a preferred embodiment, the minimum air valve, which is designed as a check valve, is a reed valve, which comprises a minimum air stop, formed as an aperture at the end of the slider, with a valve reed interacting therewith.
According to a preferred embodiment of the invention, the plurality of suction openings formed in the valve plate are arranged in a circular ring shape and can be closed by use of a suction lamella designed as a disk-shaped rotary lamella having apertures and openings. Moreover, a plurality of pressure valve cross sections formed in the valve plate can furthermore be arranged in a circular ring shape, opening within the cylinder cover into a pressure chamber with a connection to the pressure line, and can be closed alternately by the disk-shaped suction lamella. These pressure valve cross sections interact with a pressure valve unit, preferably comprising a pressure valve stop, a pressure valve spring and a pressure valve reed, which is arranged within the cylinder head on the delivery line side.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.